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SubjectRe: [PATCH 03/10] ftrace: fix sched_switch API
2008/11/8 Steven Rostedt <rostedt@goodmis.org>:
> Impact: fix for sched_switch that broke dynamic ftrace startup
>
> The commit: tracing/fastboot: use sched switch tracer from boot tracer
> broke the API of the sched_switch trace. The use of the
> tracing_start/stop_cmdline record is for only recording the cmdline,
> NOT recording the schedule switches themselves.
>
> Seeing that the boot tracer broke the API to do something that it
> wanted, this patch adds a new interface for the API while
> puting back the original interface of the old API.
>
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> CC: Frederic Weisbecker <fweisbec@gmail.com>
> ---
> kernel/trace/trace.h | 4 ++-
> kernel/trace/trace_boot.c | 6 ++--
> kernel/trace/trace_sched_switch.c | 50 +++++++++++++++++++++++++++++-------
> 3 files changed, 46 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index db12e16..25abfc4 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -324,7 +324,9 @@ void trace_function(struct trace_array *tr,
>
> void tracing_start_cmdline_record(void);
> void tracing_stop_cmdline_record(void);
> -void tracing_cmdline_assign_trace(struct trace_array *tr);
> +void tracing_sched_switch_assign_trace(struct trace_array *tr);
> +void tracing_stop_sched_switch_record(void);
> +void tracing_start_sched_switch_record(void);
> int register_tracer(struct tracer *type);
> void unregister_tracer(struct tracer *type);
>
> diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
> index 662cb91..0203c10 100644
> --- a/kernel/trace/trace_boot.c
> +++ b/kernel/trace/trace_boot.c
> @@ -28,13 +28,13 @@ void start_boot_trace(void)
> void enable_boot_trace(void)
> {
> if (pre_initcalls_finished)
> - tracing_start_cmdline_record();
> + tracing_start_sched_switch_record();
> }
>
> void disable_boot_trace(void)
> {
> if (pre_initcalls_finished)
> - tracing_stop_cmdline_record();
> + tracing_stop_sched_switch_record();
> }
>
> static void reset_boot_trace(struct trace_array *tr)
> @@ -55,7 +55,7 @@ static void boot_trace_init(struct trace_array *tr)
> for_each_cpu_mask(cpu, cpu_possible_map)
> tracing_reset(tr, cpu);
>
> - tracing_cmdline_assign_trace(tr);
> + tracing_sched_switch_assign_trace(tr);
> }
>
> static void boot_trace_ctrl_update(struct trace_array *tr)
> diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
> index fbf05df..79410db 100644
> --- a/kernel/trace/trace_sched_switch.c
> +++ b/kernel/trace/trace_sched_switch.c
> @@ -125,20 +125,16 @@ static void tracing_sched_unregister(void)
> static void tracing_start_sched_switch(void)
> {
> mutex_lock(&sched_register_mutex);
> - if (!(sched_ref++)) {
> - tracer_enabled = 1;
> + if (!(sched_ref++))
> tracing_sched_register();
> - }
> mutex_unlock(&sched_register_mutex);
> }
>
> static void tracing_stop_sched_switch(void)
> {
> mutex_lock(&sched_register_mutex);
> - if (!(--sched_ref)) {
> + if (!(--sched_ref))
> tracing_sched_unregister();
> - tracer_enabled = 0;
> - }
> mutex_unlock(&sched_register_mutex);
> }
>
> @@ -153,14 +149,48 @@ void tracing_stop_cmdline_record(void)
> }
>
> /**
> - * tracing_cmdline_assign_trace - assign a trace array for ctx switch
> + * tracing_start_sched_switch_record - start tracing context switches
> + *
> + * Turns on context switch tracing for a tracer.
> + */
> +void tracing_start_sched_switch_record(void)
> +{
> + if (unlikely(!ctx_trace)) {
> + WARN_ON(1);
> + return;
> + }
> +
> + tracing_start_sched_switch();
> +
> + mutex_lock(&sched_register_mutex);
> + tracer_enabled++;
> + mutex_unlock(&sched_register_mutex);
> +}
> +
> +/**
> + * tracing_stop_sched_switch_record - start tracing context switches
> + *
> + * Turns off context switch tracing for a tracer.
> + */
> +void tracing_stop_sched_switch_record(void)
> +{
> + mutex_lock(&sched_register_mutex);
> + tracer_enabled--;
> + WARN_ON(tracer_enabled < 0);
> + mutex_unlock(&sched_register_mutex);
> +
> + tracing_stop_sched_switch();
> +}
> +
> +/**
> + * tracing_sched_switch_assign_trace - assign a trace array for ctx switch
> * @tr: trace array pointer to assign
> *
> * Some tracers might want to record the context switches in their
> * trace. This function lets those tracers assign the trace array
> * to use.
> */
> -void tracing_cmdline_assign_trace(struct trace_array *tr)
> +void tracing_sched_switch_assign_trace(struct trace_array *tr)
> {
> ctx_trace = tr;
> }
> @@ -168,12 +198,12 @@ void tracing_cmdline_assign_trace(struct trace_array *tr)
> static void start_sched_trace(struct trace_array *tr)
> {
> sched_switch_reset(tr);
> - tracing_start_cmdline_record();
> + tracing_start_sched_switch_record();
> }
>
> static void stop_sched_trace(struct trace_array *tr)
> {
> - tracing_stop_cmdline_record();
> + tracing_stop_sched_switch_record();
> }
>
> static void sched_switch_trace_init(struct trace_array *tr)


Sorry, I misunderstood the sense of these functions and then used them only for
what they did: start/stop sched event capture.

Acked-by: Frederic Weisbecker < fweisbec@gmail.com>


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